This application requests funding for Years 26-30 of an Institutional Grant to support postdoctoral research training in transfusion medicine sciences for four trainees annually. The program, sponsored by the Blood Center of Southeastern Wisconsin (BCSEW) under the aegis of the Medical College of Wisconsin (MCW), involves close cooperation between BCSEW and the clinical and basic science departments of MCW. Senior Investigators at the Blood Research Institute (BRI) of BCSEW will serve as mentors for trainees. Richard H Aster, M.D. and Peter J Newman, Ph.D., will serve as Program Director and co-Program Director, respectively. Research Opportunities available to trainees cover a broad range on clinical and basic research subjects relevant to transfusion science, including Immunohematology, Vascular Biology, Biology and Pathophysiology of Platelets, Immunogenetics, Hemostasis/Thrombosis, and hematopoietic stem cell biology. The research training experience will be essentially till time. Trainees will be expected to gain a basic understanding of the disciplines in which they undertake their investigations, become familiar with a variety of research methodologies, and develop the ability to conduct independent research. We view time spent in fellowship training under this grant as one of several stages of professional development and offer selected trainees several additional tracks, including the opportunity 1) to apply for a Clinical Investigator Development Award (KO8) for continued mentoring, to apply for independent grant support, and 3) for those oriented toward a career in transfusion medicine, an opportunity for further training as a junior member of the Blood Center's medical staff Ultimately, trainees are expected to pursue academic careers in transfusion science or a closely related discipline such as immunohematology, transplantation immunology, hemostasis/thrombosis and stem cell biology.